Treatment of hydrocarbons



Oct. 29, 1940l R. PYzl-:L

TREATMENT OF HYDROCARBONS Filed May 31, 1938 TORNEY INVENTOR ROBERT PYZEL ma. 1| .F 3 uzjthw xzf n ne ,ozjtmw o aux.: g. ozjtmw v2 aux.: 2. n njoou .mmmmowm E mmammmmn. 01.

j Para@ oa. 29,1940

PATENT OFFICE TREATMENT F HYDROCARBONS Robert Pyzel, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application May 31, 1938, Serial No. 211,066

Claims.

'I'his invention relates to the treatment of the lower boiling range hydrocarbons produced in the cracking of the relatively heavy portions of petroleum oils.

5 It is more specifically concerned with a treatment applicable to the cracked gases and naphthas of gasoline boiling range to effect a partial purification thereof and the simultaneous production of a relatively narrow cut of normally gaseous olefin-containing hydrocarbons comprising principally 4-carbon atom hydrocarbons, which is sufficiently purified so that it exerts substantially no poisoning influence on catalysts subsequently employed to polymerize its oleflnic content and produce gasoline boiling range oleflns which are hydrogenatable to corresponding paramns of relatively high antiknock value.

Petroleum refiners are concerned at the present time with the more effective utilization of the 20 gaseous by-products of cracking petroleum fractions for the production of gasoline, and attention has been `focused especially on polymerization processes whereby liquid products boiling within the range of motor fuel are produced. These processes may operate upon the cracked gas mixtures as a whole or upon selected fractions of relatively narrow boiling range such as the so-called propane-butane -fractions of a still narrower cut comprised principally of both saturated and unsaturated four carbon atom hydrocarbons. Thus far the ethylene content of cracked gases has resisted efforts to convert it directly into gasoline boiling range liquids.

The processes employed at present in converting the three and four carbon atom hydrocarbons of cracked gaseous mixtures into gasoline boiling range material, may be roughly classified as: (1) thermal, and (2) thermal-catalytic, the latter processes operating generally at lower pressures and temperatures and being more specific in their action on the olefinic content of the gas fractions to form liquids of a purelyAmono-oleic character. When operating upon gas fractions comprising predominantly butanes and butenes, catalytic polymerizing operations may be so controlled that the major product corresponds to a mixture of dimers of the butylenes which are readily hydrogenatable to mixtures of octanes which have antiknock values approaching that of the standard iso-octane and are hence much sought after as fuel for high compression engines such as those of the airplane type.

One process which has attained extensive commercial use in polymerizn'g normally gaseous oleflns involves the use of solid granular phosphoric acid-containing cataly'sts.

Catalysts containing phosphoric acid have been found to be particularly effective in respect to their action in producing dimers and trimers of the normally gaseous oleflns in preference to polymers of higher molecular weight. However, it has been found that the effective life of these catalysts is frequently seriously reduced by the presence of relatively small amounts of impurities in the olefin-containing hydrocarbon mixtures which they are employed to treat. The exact nature of the poisoning substances is not entirely known, butsome experimental and analytical work has indicated that it may be due in part to sulfur compounds of various types and to nitrogen compounds of the nature of ammoniaor amines, these last groups being particularly damaging. 'I'hese nitrogen compounds may arise in various ways. For example, they may have been deliberately introduced into cracking plants as ammonia to reduce corrosion, or they may have resulted in the cracking of nitrogen-containing'oils which are frequently encountered in different oil fields. 'I'he present process embodies a co-operative combination of treating steps whith will both treat cracked gasolines and remove impurities from olefin-containing normally gaseous fractions intended for phosphoric acid polymerizing plants so that substantially increased catalyst life is obtained.

In one specific embodiment the' present invention comprises a process for the treatment of unstabllized cracked gasolines and the .production of maximum yields of purified butane-butylene fractions suitable for polymerization which consists of the following steps: (l) introducing cracking plant receiver gases to a high pressure absorber in which absorption is effected by debutanized naphtha; (2) introducing unstabilized cracked gasoline along with the rich high pressure absorbing oil to a depropanizer in which propane and lighter materials are removed; (3) subjecting the unabsorbed gaseous products from the high pressure absorber to further absorption in a low pressure absorber wherein the absorber oil is an intermediate fraction of cracked naphtha which is returned to the cracking plant fractionator; (4) cooling and treating the depro panized material with aqueous alkalis; (5) further fractionating the treated naphtha to produce a butane-butylene fraction as an overhead distillate; (6) washing said overhead distillate with water (preferably acidulated); (7) applying a final aqueous alkali wash to the'water washed v ploying solid phosphoric acid.

The process as above briey outlined servesvto produce a stabilized and partially purified naphtha which can then be subjected to further treatment for the production of a satisfactory gasolineI and a butane-butylene fraction which has been freed from traces of materials having a deleterious eil'ect on `phosphoric acid catalysts. It has been found thatthe sequence of steps outlined is a very practical one and that the caustic washings must be done both before and after a water wash which apparently takes out traces of compounds of an alkaline reaction such as ammonia and amines which are not effectively removed by caustic soda or other alkalis. As will be shown in later examples, the butane-butylene fractions produced by this method can be processed for extended periods of time with no eiect on the activity of the phosphoric acid catalyst than the gradual carbonizing which is always noted whereas the untreated fractions cause-a quick drop in eiliciency which necessitates a plant shut-down and the reactivation or replacement of the catalyst.

The process will be described in greater detail by reference to the attached drawing which shows in general side elevation without regard to any particular scale or relative size of the elements an arrangement of apparatus in which the process may be conducted. It will be evident that the invention is notlimited by the exact features shown but that the drawing is merely illustrative of the types of plants employed in the operation.

Referring to the drawing, cracking plant receiver gases which are separated at the primary condensation of the lighter cracked products froml a cracking plant are introduced through line I containing valve 2 to a pump or compressor 3 which discharges through a line 4 containing a valve 5 through high pressure absorber 6 which receives from line |38 containing valve |39 a portion of the debutanized pressure distillate whose production will be described in sequence at a later point. This absorber is preferably operated at a temperature of approximately F. under a pressure of 250 lbs. per square inch. The unabsorbed gases pass through line 1 containing valve 9 to a low pressure absorber 9 which operates at a pressure of approximately 50 lbs. per square inch at a temperature of 112 F. In this absorber an intermediate fraction from the nal cracking plant fractionator is preferably employed as an absorber oil, the source of this material not being shown in the drawing, though line I0 containing valve II and leading to pump I2 is indicated as a line for its admission. Pump I2 discharges into the top of the low pressure absorber through a line I3 containing a valve I4. The enriched absorber oil is withdrawn from the bottom of the low pressure absorber through line I5 containing valve I 6 and returned through line I8 containing a valve I9 by pump I1 back to the cracking plant fractionator preceding the source of the gases admitted through line I. By this method of operation substantialy all of the three and four carbon atom hydrocarbons in the cracking plant receiver gas are recovered and further processed.

The bottoms from the high pressure absorber 6 which will include all of the four-carbon atom hydrocarbons and substantially all of the three carbon atom hydrocarbons are withdrawn through line I9 containing valve 20 to a pump 2| which discharges through line 22 containing valve 23 and thence into line`21. Unstabilized crackedgasoline from the receiver of the cracking plant is introduced through line 24 containing a valve 25 to a pump 26 which discharges It will be seen from the description of the process up to this point that by the use of a combination of high pressure and low pressure absorbers and absorbing oils that practically all of the three and four carbon atom hydrocarbons produced in the cracking process will be recovered since both the cracking plant receiver gas and the liquid constituting the unstabilized cracked gasoline are processed.

'I'he preheated mixture of high pressure absorber oil and unstabilized cracked gasoline are admitted through a line 34 containing a valve 35 to a depropanizing column V36 which has an upper vapor line 31 containing a valve 38 for the release of propane and light gases. This column is preferably provided with a reboiling device which is indicated in the drawing as being a closed coil 39 having an inlet line 40 containing a valve 4I for the admission of heating fluids and an outlet line 42 containing a valve 43 for their release. This column is preferably operated at a relatively high pressure to permit effective removal of 3-carbon atom hydrocarbons and lighter compounds while retaining substantially all of the butanes and butenes. The column may be equipped with conventional reflux return to the top.

Bottoms from depropanizer 36 which will be at a temperature of approximately 360 F. are now cooled and subjected to a treatment with an alkaline aqueous solution, usually caustic soda. 'I'hus they are removed through line 44 with valve 45 closed to line 46 containing valve 41 and passed through a cooler 48 which has an inlet line 49 containing a valve 50 for the admissionof cooling liquids and an exit line 5| containing valve 52 for their release. 'I'he bottoms from the depropanizer are thus preferably cooled to a temperature of approximately F. and are then conveyed through line 53 containing valve 54 to the inlety of a mixer 55 which receives recirculated caustic soda from line |3| containing a. valve |32. 'I'he recirculated caustic soda and depropanized material passing through mixing device 55 and line 56 containing a valve 51 to settling tank 58 'is withdrawn by pump |30 by way of line |24 containing valve |25 and line |28 containing valve |29. A certain amount of the recirculated caustic is continuously wasted through line |26 containing valve I21, the makeup coming from points to be later described.

This primary caustic washing has the effect of removing-traces of hydrogen sulfide and some low boiling mercaptans from the depropanized naphtha and in the next step of the process the partially purified material passes from settling tank 58 through line 59 containing valve 60 to further fractionation. It is first heated to a temperature of approximately 210 F. during passage through a heater 6I which has a heater coil such as a steam coil with an inlet line 62l and a valve 63 and a waste line 64 containing valve 65. 'Ihe heated material follows line 66 containing valve 61 and enters line 44 leading to debutanizer 68. 75 "f l $919,599 3 It will be noted that valve 45 may be used as a by-pass valve in line 44 to permit the omission of the first caustic washing step either in whole or in part if this is found feasible.

Debutanizer 88 is preferably operated at a top temperature of 150 F. under a pressure of 100 lbs. per square inch, this column also beingprovided with a reboiling device 69 with an inlet line 10 containing a valve 1| for heating fluids and an exit line 12 containing a valve 13 for their release. The bottom temperature is maintained in the neighborhood of 300 F. The material drawn through the bottom of the column through a line 14 containing valve 15 will consist of stabilizednaphtha which is amenable to any further chemical treatment and distillation to produce a gasoline of some desired boiling range. This material is taken by pump |83 and discharged through line |34 containing valve |95. Whatever portion is not to be used as absorbing oil in the high pressure absorber is withdrawn to storage through line |38 containing valve |91. That portion which is used in the high pressure absorber is passed through line |38 containing valve |39 to the top of column 6. p

The overhead from debutanizer 88 preferably consists of 4-carbon atom hydrocarbons comprising butanes and butylenes which pass through line 18 containing valve 11, through a condenser 18 and thence through rundown line 19 containing valve to a receiver 8| which has a conventional gas release line 82 containing a valve 83. The liquid contents of receiver 8| are' taken by pump 86 by way of line 84 containing valve and distributed in part through line 81 containing valve 88- back to the top of the debutanizer to assist in controlling the composition of the emergent vapors and in part through line 89 containing valve 90 to the final purification steps.

At the entrance to mixer 9| the butane-butylene fraction meets a stream of water which is preferably slightly acid and which is supplied by pump 94 which takes suction on a source of supply through line 92 containing valve 93 and discharges through 'line 95 containing valve 96. The mixture of water and butane-butylene fraction from mixer 9| passes through line 91 containing a valve 98 to settling tank 99 which is provided with a draw-line |00 containing valve |0| for the removal of the wash water.

The apparent reason for the necessity of the water wash has already been explained. .The amount of water necessarily to effectively purify the butane-butylene fractions will vary with theY amount of water soluble materials and no absolute rules can belaid down. As a rule best results are obtained by the use of a moderately large percentage by volume and the use of water which is not alkaline as are some natural waters,

and which may be advantageously somewhat acidic.

The partially purified butane-butylene fraction from settling tank 99 passes through line |02 containing valve |03 to a third mixer |04 at the entrance of which it receives an addition of alkali solution consisting both of fresh and of recirculated material. The fresh material is taken by pump ||2 through line ||0 containing valve and discharged through line ||3 containing valve ||4 into line H5. The recirculated material comes from iinal settling tank |01 through line |08 containing valve |09. and line ||1 containing valve ||8 to pump ||9 which discharges into line ||5 containing valve ||6. The

mixture or alkali and hunne-butylene 'fraction then passes finally to settling tank |81 through line |05 containing valve |09 and may be withdrawn therefrom by way of line |88 containing valve |89 for charging to the polymerizing plants mentioned. A portion of the settled aqueous layer from tank |01 maybe passed through valves |09 and |20 in line |08"to pump |2| and discharged through line |22 containing valve |28 into the primary mixer 58 along with caustic recirculated from settling tank 08.

The following experimental data is introduced to indicate the order of improvement experienced in the use of phosphoric acid-containing polymerizing catalysts when the olefin mixture charged is treated by the process of the invention, although it is understood that the exact -comparison given only holds for one particular charge and the scope of the invention is not to be taken as limited thereby.

The receiver gas and receiver liquid constituting unstabilized cracked gasoline from a cracking plant operating on a West Texas charging stock were subjected to the cycle of operations described in'connection with the drawing, the receiver gases being introduced through a high pressure absorber wherein substantially all three and four carbon-atom hydrocarbons were absorbed by debutanized distillate and the unstabilized cracked gasoline mixed with the pressure absorber liquid, preheated and introduced into the depropanizer and subjected to the cycle of operations already described to produce a purified butane-butene fraction. When subjecting the purified material to contact with a granular solid phosphoric acid catalyst to produce a mixture of octenes from the butene content it was found that approximately gallons of liquid hydrocarbons could be produced per pound of catalyst before there was appreciable deterioration thereof as measured by the rate of conversion of olefins. The tests were conducted under conditions in the catalytic zone of approximately 330 F. and 650 lbs. per square inch pressure.

Using a butane-butene fraction originating from the same source, but produced by ordinary methods without the combination of caustic, water, and caustic washing, it was found that a production of approximately 20 gallons per pound of catalyst was all that could be obtained before there was a serious deterioration in the polymerizing capacity of the catalyst.

It is presumed in the absence of completely confirmatory data that the reason for the necessity of the intermediate water wash is due to traces of basic substances such as ammonia and amines which combine directly with the active phosphoric acid in the granular catalyst and quickly render it catalytically inert. Even though analyses show only traces of these compounds in many instances, they seriously affect the acid catalyst quite out of proportion to the quantity present.

The scope of the described invention is shown clearly by the above specification and numerical data neither of which is intended to be unduly limiting.

I claim as my invention:

1. A process for the production and purification of butene-butene fractions to render them suitable for contacting with a polymerizing catalyst which comprises subjecting. uncondensed cracked l gases to contact with debutanized cracked distillate to absorb substantial amounts of three and four carbon atom hydrocarbons,

compounds, subjecting the blend freed from saidv propane and lighter compounds to treatment with an aqueous solution of an alkali, and 'further fractionatlng'the alkali-treated blend to produce a butane-butene fraction.

2. A process for the production and purification of butane-butene fractions to render them suitable for contacting with a polymerizing catalyst which comprises subject-ing uncondensed cracked gases to contact with debutanized cracked distillate to absorb substantial amounts of three and four carbon atom hydrocarbons, blending the resultant enriched distillate absorbent with unstabilized cracked gasoline, fractionating the blend to remove propane and lighter compounds, cooling the blend freed from said propane and lighter compounds to a temperature of the order of 120 F., subjecting the cooled blend to treatment with an aqueous solution of an alkali, and further fractionating the alkali-treated blend to produce a hutane-butene fraction.

3. A process for the production and purication of butane-butene fractions to render them suitable for contacting with a polymerizing catalyst to produce substantial yields of octenes.

which comprises subjecting uncondensed cracked gases to contact with debutanized cracked distillate to absorb substantial amounts of thref` and four carbon atom hydrocarbons, blending the resultant enriched distillate absorbent with unstabilized cracked gasoline, fractionating the I blend to remove propane and lighter compounds,

cooling the fractions of said blend .-freed from said propane and lighter compounds to a temperature of the order of 120 F., subjecting said cooled fractions to treatment with a. partly spent aqueous solution oi' an alkali, separating the treated fractions from the aqueous alkali and utilizing a portion of the latter as said partly spent solution, and distilling the alkali-treated fractions to produce an overhead fraction consisting substantially only of butanes and butenes.

4. A process which comprises scrubbing cracked hydrocarbon gas with debutanized gasoline to absorb in the latter C4 components of the gas, combining the thus enriched gasoline with unstabllized cracked gasoline containing C4 hydrocarbons, treating the resultant mixture with aqueous alkali solution to separate impurities from the gasoline and from the normally -gaseous hydrocarbons contained in said mixture, and then stabilizing the thus treated mixture to remove C4 hydrocarbons. therefrom.

5. A. process which comprises scrubbing cracked hydrocarbon gas with debutanized gasoline to absorb inthe latter C4 components of the gas, combining the thus enriched gasoline with unstabllized cracked gasoline containing C4 .hydrocarbons, treating the resultant mixture with aqueous alkali solution to separate impurities from the gasoline and from the normally gaseous hydro-` carbons contained in said mixture, and then stabilizing the thus treated mixture to remove C4 hydrocarbons therefrom and supplying a portion of the stabilized mixture to the scrubbing step as an absorbent therein.

ROBERT PYZEL. 

